The present invention is directed to the scanning and storage of video images, such as letter fonts and symbols, for use in video graphics.
In the field of video graphics it is useful to store and retrieve various images to create a particular video picture. In this regard, it is particularly desirable to store and retrieve predetermined alphanumeric character fonts. A stored library of fonts enables different types of textual messages to be selectively displayed on a video screen. Of a more general nature, it is desirable to be able to extract and store all kinds of images for selective retrieval and presentation in a video graphic display. The process of storing the characteristic features of a video image is referred to as "scan-in" of that image.
A scan-in method involves the preliminary step of providing a raster scanned version of the image, e.g. a symbol or character. For example, such a version can be obtained by taking a picture of the symbol with a video camera. The raster scanned image is analyzed to determine the characteristics of the symbol, and these characteristics are stored in a library for future retrieval.
In the past, the characteristic information describing a scanned image was stored in the form of a bit map. More particularly, each pixel of a video image was analyzed to determine its red, green and blue color components. This color information for each pixel was arranged in a bit map having memory cells corresponding to the pixels of the video image. When the character was to be subsequently reproduced in a video picture the corresponding pixels in the appropriate portion of the picture were controlled in accordance with the information in the bit map.
The bit map approach to storing scanned image information poses certain limitations if the image is to be reproduced at a size other than that at which it was originally scanned in. For example, if it is desirable to reduce the size of the displayed image to 1/4 of the original scanned size, the information concerning each group of four pixels in the bit map must be reduced to a single pixel in the displayed image If two of the original four pixels represent white and the other two represent black, it will be appreciated that some form of decision making criteria must be established to determine whether the single pixel in the displayed image is to be white or black. Regardless of which choice is made, the displayed image will not have the full integrity of the original scanned image. Typically, a relatively complex filtering procedure is utilized to carry out a reduction or amplification in the size of a video image. Even with such procedures, however, a loss in the integrity of the image occurs because arbitrary decisions of the type referred to above must be made.
In the field of video graphics, it is often more desireable to store information concerning an image in terms of its geometry, i.e. by means of vector representations, rather than in a pixel-related bit map. The vector information can be more easily modified to change the size of an image without losing the integrity of the image. In the past, however, vector representation has not been done with images which are extracted from a video frame, such as character fonts and symbols.
Further along these lines, the vector representation approach more readily facilitates the editing of character images. For example, it may be desirable to change the geometry of a stored character in order to smooth out a sharp corner or the like. In the bit-map approach, this change is performed by modifying the value of a bit. This type of change may become readily apparent and appear awkward when the size of the character is subsequently changed, particularly if it is enlarged. However, changes in the geometry of an image that is stored in terms of vector representations are more easily accommodated.
Another advantage of the vector representation of video images lies in the fact that the information about the image is more easily transferred from one video machine to another. Geometric information can be readily interpreted and sent to various machines in a consistent fashion. However, pixel arrangements may vary from machine to machine, so that a bit mapped image that is extracted on one machine may not be accurately reproduced on another machine.